Tunable magnetron



March 21, 1950 c, w, BECKER 2,501,152

TUNABLE MAGNETRON Filed Sept. 5, 1946 H 40 T 2 2 EXTERNALLV APPLIED -Q\2 0 CONTROL S/GNAL @V 7+ l 3 a.

sea 30 L -35 /NVENTO/? (74/21. W BE KER BY AT Patented Mar. 21, 1950UNITED STATES TUNABLE MAGNETRON Application September 5, 1946, SerialNo. 695,022

6 Claims.

This invention relates to electron-discharge devices, and moreparticularly to tunable electron-discharge devices.

While not limited thereto, the present invention is especially suitablefor tunable electrondischarge devices of the so-called magnetron type.

This invention constitutes an improvement over that described in mycopending application, Ser. No. 586,969, filed April 6, 1945. In saidcopending application, a remotely-controlled means for tuning a deviceof the magnetron type is disclosed, this means comprising a core or reedmounted for movement with respect to the anode of said magnetron, saidcore or reed having mounted thereon a coil which is located in theleakage magnetic field of said device and is adapted to be supplied witha signal or control voltage to move said core or reed.

An object of this invention is to provide means for concentrating theleakage magnetic flux of the magnetron in the region thereof in whichthe said coil is located, whereby the magnetic field strength in saidregion is increased, resulting in a greater displacement or movement ofsaid tuning means for a given control voltage.

Another object is to increase the effective sensitivity of avoltage-controlled magnetron tuning device.

The foregoing and other objects of the invention will be best understoodfrom the following description of an exemplification thereof, referencebeing had to the accompanying drawing, wherein:

Fig. 1 is a longitudinal. sectional view taken substantially through thecenter of a tunable magnetron made in accordance with the principles ofthe present invention; and

Fig. 2 is a transverse sectional View, partly broken away to showdetails, taken along line 22 of Fig. 1.

Referring now more in detail to an illustrative embodiment of thepresent invention. with particular reference to the drawing showing thesame, the numeral l generally designates an electron-discharge device ofthe so-called magnetron type. Said device comprises an anode structure2, a cathode structure 3, magnetic means ii for establishing a magneticfield in a direction perpendicular to the path of the electron-flowbetween said cathode and anode structures, and tuning means 5.

In the device shown, the anode structure 2 includes a cylindrical body 6made of highly conductive material, such as copper, said bod beingprovided with an interior, annular boss 65', in turn provided with amultiplicity of radially-disposed, interiorly-extending anode members inthe form of vanes 7, each adjacent pair of said vanes, together withthat portion of said cylin-= drical body lying therebetween,constituting a resonant line, preferably, a quarter-wave line whoseoutput end is shorted, and whose natural resonant frequency is, as iswell-known in the art to which this invention relates, a function of thegeometry of the physical elements making up the same. I shall furtherdescribe the anode members i when referring, in a later portion of thisspecification, to the details of the tuning means 5.

The anode structure 2 is closed at its ends, for example, by end plates8 and 9, with the junctions between the cylindrical body t of saidstructure, and said plates ii and 9, hermetically sealed, as at Ill.

The cathode structure 3, which is coaxial with the anode structure 2,includes a cathode sleeve H, conventionally made of nickel, or the like,provided with a reduced portion l2 whose length, preferably, iscoextensive with the width of the anode members i, said reduced portionl2 being provided with a highly electron-emissive coating l3, forexample, of the well-known alkaline-earth metal oxide type.

Cathode sleeve H may be reduced, as at M, to fit into an elongated,electrically-conductive tubular member l5. A glass seal (not shown) atthe outer end of member l5, together with one or more glass beads (notshown) disposed within the tubular member l5, supports a leadinconductor 56 which passes through said member 15 and has its upper endconnected, as at ii, to one terminal of a cathode heating filament 8.The other end of said filament may be connected, as at l 9, to thecathode sleeve I I.

In order to convey current to the filament it, the lead-in conductor itis connected by a conductor (not shown) to one terminal of a suitablesource of E. M. F. (not shown), the other terminal of said source of E.M. F. being connected by a conductor (not shown) to the lower end of thetubular member i5.

The cathode 3 may be properly supported, and insulated from the anodestructure 2, by any suitable supporting and insulatin means, for exampleas shown in my aforesaid copending application. This supporting andinsulating means may include a tubular bushing 28 secured to a tubularpole piece 2 l, constituting one of the components of the magnetic means3.

Said pole piece 21 may be hermetically sealed, as at 22, into the endplate 8, and he provided with a central bore 23 whereby the cathodestructure 3 may enter the device.

Another tubular pole piece it may be hermetically sealed, as at 25, intothe end plate 53, said pole piece and the pole piece 2! being fixed, forexample, to the opposite ends of a horseshoe magnet 26 (only partiallyshown), whereb an appropriate magnetic field may be established, as

3 previously indicated, in a direction perpendicular to the path of theelectron-flow between the cathode structure 3 and the anode structure 2.

Now, by suitably heating the cathode, and applying a proper potentialdifference between said cathode and the anode, the device can be made togenerate electrical oscillations of a wavelength determined, primarily,by the capacitance and inductance built into said device as a functionof the geometry thereof, and, more especially, of the dimensions of theabove referred to resonant lines defined by the anode structure.

In order to extract power from the device I may, for example, introducea loop 27 into any one of the spaces defined by any two adjacent anodemembers I, said loop coupling with the magnetic component of theabove-mentioned electrical oscillations. Said loop may, in turn, beconnected to a conductor 28 supported in a glass seal 29 fused into anoutlet pipe 30, said pipe being threaded and hermetically sealed intothe cylindrical body 6 of the anode structure 2.

Each anode member is provided with a slot 31 adapted to receiveconcentric conducting straps 32 and 33 which are, in turn, adaptedalternately to contact successive anode members. Said straps present acapacitance therebetween which enters into the determination of anatural resonant frequency of the device, and when the anode members arethus inter-connected, spurious oscillations which might exist in thedevice become suppressed.

It has been found that, by moving another conducting member with respectto the anode members I, or with respect to the straps 32 and 33 thereof,the distributed capacitance or, with appropriate modifications, thedistributed inductance, of the device, or both, may be altered wherebysaid device may be tuned to frequencies other than the natural resonantfrequency thereof, and to this end, I proceed as follows:

I provide said additional conducting member, for example, in the form ofan annular fiange 34 formed at the lower end of a hollow, cylindricalcore or reed 35. Said core or reed depends from a diaphragm 36 which issecured, at its periphery, in a recess formed in the upper surface of asupporting ring member 31. Diaphragm 36 has formed therein, between itsperiphery and the cylindrical reed 35, a corrugation 38a, in order tomake diaphragm 36 more flexible.

Ring member 3'! is made of ferromagnetic material, for example iron, isof substantial thickness, and is mounted within the body 6 upon theledge presented by the boss 6' thereof. Said ring member has a recess 38cut in the lower surface thereof.

Wound upon the core and firmly secured thereto is a coil 39 of insulatedwire, one end, 39, of said coil being electrically connected to thecore, and the other end thereof passing through a suit able opening inmember 31, beyond the periphery of diaphragm 36, and out of the device,through a glass seal 40 fused into a pipe 4! which is hermeticallysealed into the end plate 9. Member 31 has a central aperture 42extending entirely therethrough, this aperture being of sufiicient sizeto allow free movement therein of core 35 and coil 39.

Core or reed 35, coil 39 carried thereby, and ring 31 should be sodisposed with respect to the pole piece 24 that said coil and said ringare within the leakage field existing between said pole piece 24 and thepole piece 2|. Hence, upon application of an external signal betweenconductors 43 and 44, respectively connected to the coil 39 and body 6,the current flowing in said coil, and the leakage field above referredto, interact to move said core, and the flange 34 carried thereby, withrespect to the anode members ii. The result of this movement is, aspreviously indicated, an alteration of the distributed capacitance ofthe device, and a consequent tuning thereof.

Ferromagnetic or iron ring member 3'1", being in the leakage magneticfield existing between pole pieces 2| and 24, acts to concentrate themagnetic flux in the region defined by the cylindrical face of aperture42, thus increasing the field strength in this region. This occursbecause of the low reluctance of the flux path through member 3?, ascompared to the reluctance of the path through the surrounding air, sothat the flux density in member 31 becomes quite high, giving a highfield strength or magnetic intensit in the space between member 37 andthe cylindrical face of upper pole piece 24. In a typical case, it wasfound that the field strength in the gap adjacent pole piece 2 3 was ofthe order of 5000 gauss without the iron ring 37; with an iron ring thefield strength was of the order of 8,000

gauss.

Coil 39 is located in the air gap between member 31 and pole piece 2%,so that it is in this magnetic field of said high field strength.Therefore, since the force on a current-carrying conductor in a magneticfield is directly proportional to the field strength or magneticintensity H, the force on coil 39 will be increased, for the sameexcitation, by the addition of flux concentrating means 37 due to theincrease of H by said means. As a result, a high displacement-voltagesensitivity for coil 38 is obtained in accordance with the teaching ofthis invention.

If desired, damping means may be provided on core or reed 35 to damp outthe natural resonant vibratory frequency of said reed. in accordancewith the teachings of my copending application, Ser. No. 694,056, filedAugust 30, 1946.

This completes the description of an embodiment of the invention. Itwill be noted from all of the foregoing that I have devisedflux-concentrating means, for an electromagnetically-operated magnetrontuning means, which is relatively simple in construction yet hi hlyeffective to pro vide a high sensitivity for the said tuning means.

Of course, it is to be understood that this invention is not limited tothe particular details as described above, as many equivalents willsuggest themselves to those skilled in the art. It is accordinglydesired that the appended claims be given a broad interpretationcommensurate with the scope of this invention within the art.

What is claimed is:

l. The combination with an electron discharge device which incorporatesa cathode, an anode spaced from said cathode, and means for establishinga magnetic field in a direction substantially perpendicular to the pathof the electron fiow between said cathode and said anode, said deviceproducing oscillations having a natural resonant frequency determin d bythe configuration of said device: of means, supported within said deviceand movable with respect to said anode, for tuning said device to afrequency other than said natural resonant frequency; means, supportedby said movable means within the magnetic lines of force of saidmagnetic field and receptive of an external signal,

for establishing a signal-responsive magnetic field cooperable with saidlines of force for controlling the operation of said tuning means; andmeans, supported within said device near said controlling means andwithin said magnetic lines of force, for increasing the flux density ofsaid magnetic field in the vicinity of said controlling means.

2. The combination with an electron discharge device which incorporatesa cathode, an anode spaced from said cathode, and a pair ofoppositely-disposed means for establishing a magnetic field between saidanode and said cathode in a direction substantially perpendicular to thepath of the electron flow between said cathode and said anode, saiddevice producing oscillations having a natural resonant frequencydetermined by the configuration of said device: of means, supportedwithin said device and movable with respect to said anode, for tuningsaid device to a frequency other than said natural resonant frequency;means, supported by said movable means near one of said magnetic means,within the magnetic linesof force of said pair of magnetic means andreceptive of an external signal, for establishing asignal-responsive'mag-. netic field cooperable with said lines of forcefor controlling the operation of said tuning means; and means, supportedwithin said device near said controlling means and within said magneticlines of force, for increasing the flux density of said magnetic fieldin the vicinity of said controlling means and of said one magneticmeans.

3. An electron discharge device, comprising a cathode, an anode spacedfrom said cathode, a pair of oppositely-disposed means for establishinga magnetic field between said anode and said cathode in a directionsubstantially perpendicular to the path of the electron flow betweensaid cathode and said anode, said device producing oscillations having anatural resonant frequency determined by the configuration of saiddevice, means supported within said device for tuning said device to afrequency other than said natural resonant frequency, means surroundingbut spaced from one of said magnetic means and within the magnetic linesof force of said pair of magnetic means, said last-named means beingreceptive of an external signal for establishing a signal-responsivemagnetic field cooperable with said lines of force to control theoperation of said tuning means, and means, surrounding said controllingmeans and within said magnetic lines of force, for increasing the fluxdensity of said magnetic field between said controlling means and saidone magnetic means.

4. An electron discharge device, comprising a cathode, an anode spacedfrom said cathode, a pair of oppositely-disposed cylindrical pole piecesfor establishing a magnetic field between said anode and said cathode ina direction substantially perpendicular to the path of the electron flowbetween said cathode and said anode, said device producing oscillationshaving a natural resonant frequency determined by the configuration ofsaid device, means supported within said device for tuning said deviceto a frequency other than said natural resonant frequency, meanssurrounding but spaced from one of said pole pieces and within themagnetic lines of force of said pair of pole pieces, said last-namedmeans being receptive of an external signal for establishing asignal-responsive magnetic field cooperable with said lines of force tocontrol the operation of said tuning means, and means, surrounding saidcontrolling means and within said magnetic lines of force, forincreasing the flux density of said magnetic field between saidcontrolling means and said one pole piece.

5. .An electron discharge device, comprising a cathode, an anode spacedfrom said cathode, a pair of oppositely-disposed cylindrical pole piecesfor establishing a magnetic field between said anode and said cathode ina direction substantiall perpendicular to the path of the electronflowbetween said cathode and said anode, said device producingoscillations having a natural resonant frequency determined b theconfiguration of said device, means supported within said device fortuning said device to a frequency other than said natural resonantfrequency, means surrounding but spaced from one of said pole piecesandwithin the magnetic lines of force of said pair of pole pieces, saidlast-named means being receptive of an external signal for establishinga signal-responsive magnetic field cooperable with said lines of forceto control the operation of said tuning means, and means, surroundingbut spaced from said controlling means and within said magnetic lines offorce, for increasing the flux density of said magnetic field betweensaid controlling means and said one pole piece, and between saidflux-density-increasing means and said controlling means.

6. An electron discharge device, comprising a cathode, an anode spacedfrom said cathode, a pair of oppositely-disposed cylindrical pole piecesfor establishing a magnetic field between said anode and said cathode ina direction substantially perpendicular to the path of the electron flowbetween said cathode and said anode, said device producing oscillationshaving a natural resonant frequency determined by the configuration ofsaid device, means supported within said device for tuning said deviceto a frequency other than said natural resonant frequency, meanssurrounding but spaced from one of said pole pieces and within themagnetic lines of force of said pair of pole pieces, said last-namedmeans being receptive of an external signal for establishing asignal-responsive magnetic field cooperable with said lines of force tocontrol the operation of said tuning means, and a ferromagnetic member,surrounding but spaced from said controlling means and within saidmagnetic lines of force, for inpiece, and between saidflux-density-increasing means and said controlling means.

CARL W. BECKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,312,919 Litton Mar. 2, 19432,419,172 Smith Apr. 15, 1947 2,422,465 Bondley June 17, 1947 2,444,435Fisk Jul 6, 1948 FOREIGN PATENTS Number Country Date 537,518 GreatBritain -l June 25, 1941

